1. Field of the Invention
The present invention relates to an image scanning apparatus scanning an original to detect a predetermined pattern included in the original.
2. Description of the Related Art
In recent years, for the purpose of preventing unauthorized copy of an original, an image scanning apparatus having bill recognition capability or security screen pattern capability has been developed.
The bill recognition is a technology of determining whether or not an original is a special one such as bill or valuable paper. The bill recognition is generally achieved by examining whether or not image data obtained by scanning an original includes a specific pattern.
Further, the security screen pattern is a technology of printing in advance, on an original image, a character string or the like such as “copy prohibited” as a screen pattern that reappears on a copy of the original. The security screen pattern can prevent unauthorized copy of a confidential document. Japanese Laid-Open Patent Publication No. 2005-142917 discloses an image processing apparatus that determines, based on the dot density of image data, whether or not the image data obtained by scanning an original with a scanner is a confidential document.
The image scanning apparatus thus scans an original to determine whether or not the original includes a pattern specific to a bill or a predetermined pattern such as screen pattern. The image scanning apparatus can use the result of the determination to prevent unauthorized copy of the original.
Consideration will be given here to an original whose opposing two sides are both printed with respective images. It is supposed that, if at least one side of the original is printed with a predetermined pattern as described above, the images on the opposing two sides are intended to be prevented from being copied unauthorizedly. Actually, however, an apparatus scanning only one side of the original can scan the side without the predetermined pattern. Therefore, in order to surely determine whether or not the original includes the predetermined pattern, it is necessary to scan both sides of the original.
A method for scanning both sides of an original is to combine one-side scanning and reversal of an original.
Another method for scanning both sides of an original is to use an image scanning apparatus including two scanning units (first scanning unit and second scanning unit). According to this method, the image scanning apparatus scans a first side of the original using the first scanning unit, and scans a second side of the original using the second scanning unit. This method is hereinafter referred to as simultaneous double-side scanning. The simultaneous double-side scanning requires a large-sized apparatus including two image scanning units. The simultaneous double-side scanning, however, can shorten the time required for scanning. The simultaneous double-side scanning is therefore widely used.
Some image scanning apparatuses for use in simultaneous double-side scanning include a scanning unit configured with a combination of a CCD (Charge-Coupled Device) and a CIS (Contact Image Sensor).
The CCD scans, via a reduction optical system, the light that is emitted from a light source such as halogen lamp or xenon bulb lamp to an original and reflected from the original. The CIS scans the light emitted from an LED (Light Emitting Diode) light source to an original where the size of the scan light is identical to the original size.
Scanning with the CIS is shallower in depth of field as compared with scanning with the CCD, resulting in an out-of-focus state even when the fed original is displaced to a slight degree. Thus, the accuracy of scanning with the CIS is low. In the case of scanning with the CCD, however, an optical system has to be provided between an original and the CCD. Thus, scanning with the CCD has a disadvantage that a large space is necessary. Both the high scanning accuracy and the downsizing of the apparatus can be accomplished by combining the CIS scanning and the CCD scanning.
Japanese Laid-Open Patent Publication No. 2007-074500 discloses an image scanning apparatus having an original reversal mechanism. The image scanning apparatus disclosed in Japanese Laid-Open Patent Publication No. 2007-074500 includes a CCD scanning unit and a CIS scanning unit. The CCD scanning unit can scan both of a monochrome image and a color image. While the CIS scanning unit can scan a monochrome image only, the CIS scanning unit can determine whether a scan image is a monochrome image or color image. Only in the case where the image scanned by the CIS scanning unit is a color image, the image scanning apparatus reverses the original and scans the original again. In this way, the image scanning apparatus can efficiently scan a plurality of originals including a color image and a monochrome image.
Japanese Laid-Open Patent Publication No. 2005-012442 discloses an image scanning apparatus performing the simultaneous double-side scanning with a CCD and a CIS in a speed-priority mode. This image scanning apparatus scans the front side and the rear side of an original using the CCD in an image-quality-priority mode.
If the simultaneous double-side scanning technology by means of the CIS and CCD in combination is directly applied, it may not be accurately determined whether or not an original includes a predetermined pattern, because the accuracy of scanning with the CIS and the accuracy of scanning with the CCD differ from each other.